Method of degassing and solidifying an aluminum alloy powder

ABSTRACT

The object is to provide a method of degassing or solidifying an aluminum alloy powder by utilizing an induction heating as a degassing means in a step of forming and solidifying an aluminum powder or aluminum alloy powder, whereby the disadvantages of the prior art can be overcome. The feature of the present invention consists in preforming an aluminum powder, aluminum alloy powder or aluminum composite alloy powder or mixed powders thereof with non-metallic grains to give a specific electric resistance of at most 0.2Ωcm, subjecting the preform directly to induction heating in an atmosphere at normal pressure, temperature-raising to 400° to 600° C. at a temperature gradient of at least 0.4° C./sec in a temperature range of at least 300° C. and removing heat-decomposable volatile components to obtain a hydrogen content of at most 10 ppm.

TECHNICAL FIELD

This invention relates to a method of degassing and solidifying arapidly solidified aluminum alloy powder.

BACKGROUND TECHNIQUE

As a method of forming and solidifying a rapidly solidified aluminumalloy powder, there are various methods, for example, extrusion method,HIP method, powder forging method, etc. For solidifying a powder, it isnecessary to heat the powder by all means, during which the quenchingeffect of the powder is lost to deteriorate the properties. Preventionof this deterioration is carried out by rapidly heating in a short time.A patented invention relating to carrying out rapidly heating for thepurpose of solidifying a rapidly solidified aluminum alloy powder is 1.U.S. Pat. No. 4,435,213: "Method for Producing Aluminum Powder AlloyProducts Having Improved Strength Properties; Alcore", a patentedinvention relating to induction heating of general powders, not limitedto aluminum, is 2. U.S. Pat. No. 5,134,260: "Method and Apparatus forInductively Heating Powders or Powder Compacts for Consolidation;Carnegie Melon University" and a patented invention relating to rapidlyheating by hot air is 3. Japanese Patent Laid-Open Publication No.158401/1991: "Method of Heating Rapidly Solidified Powders; Kubota".

To any one of the above described powder forging method, extrusionmethod and HIP method, well known in the art, is indispensable theheating before solidification because of 1. decreasing a deformationresistance of a powder and shaping the powder with a low stress and 2.degassing.

In particular, the degassing is an indispensable means for preventing asolidified article from forming of bubbles called blistering and in thecase of the powder forging, strongly bonding grains with each other, forexample, like known methods described in Japanese Patent Laid-OpenPublication No. 224602/1987 and "Kei-Kinzoku (Light Metals)" 37 (10)1987, page 656-664.

In the prior art techniques, degassing has generally been carried out bycan-sealing a CIP (cold isotactic pressing) body and heating in vacuumor in an inert gas atmosphere at a temperature of 400° to 600 ° C. Anyprior art method has aimed at completing sufficiently degassing byraising the temperature for 0.5 to 2 hours and maintianing apredetermined temperature for 0.5 to 2 hours, amounting to 1 to 4 hours,using an ordinary resistance heating furnace.

However, it has hitherto been pointed out that the above describeddegassing method has the disadvantages that the quenching effect of apowder, i.e. the effect of precipitating finely and unifromly an elementor phase which tends to be coarsely precipitated at an ordinary coolingrate or the effect of rendering crystal grains fine is lost by heatingfor a long time to deteriorate the properties of a shaped and solidifiedbody, and moreover, prevention of oxidation during then needscontrolling of the atmosphere, resulting in rising of the productioncost.

Heating rapidly and uniformly a material having a low heat conductivitysuch as green compacts has generally been considered difficult.Ordinarily, the most suitable method for rapid heating on a commercialscale is an inductive heating. For example, it has been reported inJapanese Laid-Open Publication No. 134503/1974 that for powdermetallurgy of a ferruginous metal, a high frequency induction heating isutilized for heating and sintering a green compact. Up to the presenttime, such a high frequency inductive heating has been utilized forprevious heating in sintering in a shorttime or sintering forging(forging for increasing the density of a preform which is beingsintered).

However, the inductive heating has not been used for degassing of agreen compact of aluminum powder or aluminum alloy powder. The reasonstherefor are as follows:

It has been considered that the presence of a stable alumina film (Al₂O₃) with a low electric conductivity on surfaces of aluminum powder oraluminum alloy powder results in increase of the resistance of thepowder and decrease of the electric conductivity of a green compact andan effective heating is impossible by induction heating since Joule'sheat is hard to be generated in a material with a low electricconductivity, such as aluminum, eddy current is hard to be generated inthe green compact and aluminum itself has a smaller magneticpermeability different from ferruginous materials.

Furthermore, it has been considered that even if the induction heatingof the powder pressed compact can be carried out, a temperaturedifference between the surface and central part thereof is so large dueto the low heat conductivity thereof that it is impossible to heat at auniform temperature.

Under the situation, the present invention provides a method ofdegassing aluminum powder or an aluminum alloy powder comprisingutilizing induction heating for a degassing means in a step of formingand solidifying the aluminum powder or aluminum alloy powder, wherebythe above described disadvantages of the prior art can be overocme.

When solidifying a rapidly solidified aluminum alloy powder, thefollowing subjects should be taken into consideration:

(A) A thermal history added to a powder is minimized so as to minimizedeterioration of the texture of the powder by heating forsolidification.

(B) Bonding of aluminum powder with each other is rendered as strong aspossible.

(C) The solidification is carried out with a low cost.

Above all, for accomplishing the subject (A), the rapid heating methodby the induction heating or hot air heating method as disclosed in theforegoing three patents is favourable. In the rapid heating method,however, there arises a problem that the bonding of aluminum powder witheach other [subject (B)] is hard to take place. Therefore, the heatingin the air, as described in Example of the patent 1, results in loweringof the fracture elongation even if the extrusion is carried out. For thepurpose of compensating this subject, it is required to carry out therapid heating in an inert gas, to carry out vacuum degassing before thesolidification and to increase the elongation or fracture toughnessvalue of the solidified material by extrusion or swageing working tocause a large plastic deformation after the solidification. In thepatent 3, an apparatus for rapid heating in vacuum is provided. However,the subject (C), i.e. solidification with a low cost cannot beaccomplished by addition of these steps.

The present invention provides means for solving the above describedsubjects (A), (B) and (C) and provides a solidified body having a higherstrength and toughness without lowering mechanical properties ascompared with any of solidifying methods of the prior art and asolidifying method for obtaining the same in economical manner.

DISCLOSURE OF THE INVENTION

The inventors have made various studies to solve the above describedproblems and consequently, have found a method whereby degassing ofaluminum or aluminum alloy powder can be carried out with suppressingdeterioration thereof by the use of induction heating and the heatingtime can be decreased to about 1/10 of the prior art. The presentinvention is based on this finding.

Accordingly, the present invention provides a method of degassingaluminum powder, aluminum alloy powder or aluminum composite alloypowder or mixed powders thereof with non-metallic grains, beforesolidification thereof, characterized by preforming the powder body togive a specific electric resistance of at most 0.2Ωcm, subjecting thepreform directly to induction heating in an atmosphere at normalpressure, temperature-raising to 400° to 600° C. at a temperaturegradient of at least 0.4° C./sec in a temperature range of at least 300°C., and removing heat-decomposable volatile components to obtain ahydrogen content of at most 10 ppm.

In the present invention, the above described induction heating can becarried out in the atmosphere.

In the present invention, moreover, readsorption of moisture can beprevented by, after degassing by the above described induction heating,cooling the preform in an inert gas atmosphere.

In addition, the inventors have made various studies to solve the abovedsecribed problems and consequently, have found that the followingprocedures, differing from the prior art, are the most suitable forachieving the above described subjects (A), (B) and (C), leading to thepresent invention.

(i) As to heating of the powder, rapid heating is employed as usual, butthe heating temperature is maintained at at least 30° C. higher than inthe prior art.

(ii) As to solidifying of the powder, it is preferable to use a powderforging method, not a HIP method nor extrusion method.

(iii) The atmosphere for rapid heating should be not vacuum nor inertgas atmospheres, but inexpensive stagnant atmospheres at normal pressure(the stagnant atmosphere).

(iv) Rapid cooling is carried out after powder forging.

That is, the feature of the present invention consists in preformingaluminum powder, aluminum alloy powder or aluminum composite alloypowder or mixed powders thereof with non-metallic grains to give aspecific electric resistance of at most 0.2 Ωcm, subjecting the preformdirectly to induction heating in a stagnant atmosphere at normalpressure, maintaining a temperature-raising gradient of at least 0.4°C./sec at a temperature range of at least 300° C., temperature-raisingto 400° to 600° C. corresponding to a temperature of at least 30° C.higher than the vacuum degassing temperature applied to a case ofextruding the above described powder, removing heat-decomposablevolatile components to obtain a hydrogen content of at most 10 ppm, thendirectly subjecting a product to hot working and thus solidifying theproduct.

As to the heating temperature, a higher temperature, i.e. 400° C. to themelting point can be chosen in the case of an alloy containing only analloying element (Fe, Ni, etc.) which does not lower the melting pointof Al (MP 660° C.). As a preferred embodiment of the present invention,a powder forging method can be used as the above described hot working.

In the present invention, the above described induction heating can becarried out in the inexpensive stagnant atmosphere and moreover, boththe strength and toughness can more be improved than in the prior artwithout degassing in vacuum before solidifying, without subjecting toplastic working such as extrusion after solidifying and without loweringthe elongation and fracture toughness.

Furthermore, the feature of the present invention consists in quenchingat a rate of at least 10° C. immediately after forging, or reheating ata temperature of at most the forging temperature and at least (theforging temperature -50° C.) without cooling to room temperature andsubjecting to a quenching and solution treatment.

In addition, a particularly preferable embodiment of the presentinvention comprises carrying out the preforming of the above describedpowder after coating the inner wall of a metallic mold with a wettingagent without adding an organic wetting agent to the powder.

Infrared radiation heating or direct electric heating can also be usedinstead of the above described induction heating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an SEM photograph instead of a drawing of a texture of aforged body obtained in Example 2-1) of the present invention.

FIG. 2 is an SEM photograph instead of a drawing of a texture of aforged body obtained in Example 2-3) of the present invention.

FIG. 3 is an SEM photograph instead of a drawing of a texture of aforged body obtained in Comparative Example 2-6) of the presentinvention.

BEST EMBODIMENT FOR CARRYING OUT THE INVENTION

Considering that it is difficult to heat the whole body of a greencompact at a uniform temperature in a short time, heating for a longtime, e.g. at least 1 hour has ordinarily been carried out using aresistance heating furnace up to the present time, but the quenchingeffect of a powder is lost because of being exposed to the hightemperature for a long time, as described above. Since H₂ O component inthe air hinders the above dscribed H₂ O release reaction and O₂component in the air oxidizes the powder, moreover, the heating hasgenerally been carried out in vacuum, in a low dew point and low O₂concentration atmosphere or in an inert gas atmosphere so as to preventthis phenomenon.

On other hand, according to conditions found as a result of theinventor's studies, it is rendered possible to rapidly heat a formedbody of aluminum powder or aluminum alloy powder by induction heatingwhich has hitherto been considered unsuitable and to effect sufficientdegassing even by induction heating in the air, since removal ofadsorbed water or crystallization water can sufficiently be effected byheating in a short time and because of shortening of the heating time,the contact time with the atmosphere at a high temperature is short.

That is, the above described conditions are that the compacting pressureof a pressing mold is increased by about 20 % as large as the prior artso as to increase electric contact of a powder with each other, and anincident direction of magnetic induction flux of a high frequency andthe frequency of the high frequency are selected to be optimum.

Examples of the aluminum alloy powder used in the present inventioninclude not only the rapidly solidified alloy powders but also thoseprepared by any other methods. The composition thereof is not limited,but can be an aluminum composite alloy powder (aluminum or aluminumalloy powder in which a nonmetallic or intermetallic compound isdispersed). Aluminum powder can also be used. In addition, non-metallicgrains such as SiC or Al₂ O₃ grains can be mixed with these powders.

Firstly, aluminum powder, aluminum alloy powders, aluminum compositealloy powders or mixed powders thereof with non-metallic grains arerespectively formed into a preform with an increased density to give aspecific electric resistance of at most 0.2Ωcm. The forming in this casecan be carried out by a mold pressing method such as uniaxialcompression method, a CIP method or other methods, without usingheat-decomposable organic lubricants. The powder grains are thus subjectto micro-shearing forces with each other so that they have metalliccontact areas with each other.

When the specific electric resistance exceeds 0.2 Ωcm, eddy current ishard to flow and the temperature of the preform is not readily raisedeven by induction heating. If an output of an electric source isincreased to fast raise the temperature, the temperature gradientbetween the surface of the preform and interior part thereof isincreased due to low heat conductivity of the preform with the largeelectric resistance value and cracks tend to occur due to thermalstrain. The specific electric resistance of at most 0.2 Ωcm cangenerally be accomplished by a compacting pressure of 4 to 6 tons/cm².When this is not accomplished within this range, the mold pressing iscarried out at a high pressure or after the temperature of the powder israised to decrease a deformation resistance thereof.

The preform is then subjected directly to induction heating using anelectric source and rapidly heated at 400° to 600° C. while maintaininga temperature-raising rate of 0.4° C./sec at a temperature of at least300° C., during which the frequency is preferably adjusted to 3 kHzaccording to the inventor's experiment, although an optimum frequencycan suitably be chosen depending on a subject to be heated.

During solidifying a rapidly solidified powder, its behaviours of theinterior part and surface part are different. That is, the interiorstate mainly governs a tensile strength and hardness, so if the thermalhistory for solidification is reduced, the tensile strength and hardnessof the powder itself are naturally increased. On the other hand,properties such as fracture elongation and fracture toughness are mainlygoverned by the surface state of the rapidly solidified powder.

An oxide film, i.e. alumina (Al₂ O₃) on the surface of the aluminumpowder is such a stable compound that is hardly removed by reduction.This oxide film hinders strong bonding of the aluminum alloy powdergrains with each other. Accordingly, there has been proposed a methodcomprising subjecting the powder to a plastic flow working, e.g.extrusion or upset working, thus meachanically breaking the oxide film,exposing and bonding fresh surfaces of aluminum. It has been known upto-the present time, however, that even when using the extrusion method,there is obtained only a product with a low elongation and low fracturetoughnes value if degassing before the solidification is insufficient.Now, the degassing method will be illustarted:

A gas-atomized and rapidly solified aluminum alloy powder has an oxidefilm with a thickness of 50 to 100Å covered on the surface thereof, thesurface oxide film further containing adsorbed water or crystallizationwater, which causes lowering of the elongation or fracture toughnessvalue of the solidified material.

These water componets can be removed by the following reactions:

    H.sub.2 O (liq)→H.sub.2 O (gas)

    Al.sub.2 O.sub.3.3H.sub.2 O→Al.sub.2 O.sub.3.H.sub.2 O+2H.sub.2 O (gas)

    Al.sub.2 O.sub.3.H.sub.2 O→Al.sub.2 O.sub.3 +H.sub.2 O (gas)

This removal reaction takes place at 100° to 400° C. and at atemperature of 300° C. or higher, water vapor generated by the abovedescribed reaction directly reacts with aluminum to evolve hydrogen.That is, thew following reaction takes place,

    2Al+3H.sub.2 O→Al.sub.2 O.sub.3 +3H.sub.2 (gas)

A method having been employed to accelerate these reactions comprisesheating for a long time (longer time allows to proceed more reactions),heating in vacuum (lower atmospheric pressure results in tendency ofproceeding of these reactions to right) or heating in an inert gas witha low dew point (these reactions tend to proceed to right because ofless H₂ O (gas) at a low dew point). The object of using the inert gasatmosphere is to prevent the powder from oxidation.

From this point of view, it can be understood that rapid heating iseffective for breaking the structure of the interior part of the powderbut is disadvantageous from such a point of view that release of thewater adsorbed on the surface oxide film of the powder and thecrystallization water is accelerated. It is probably due to this reasonthat in Examples 1 and 2 of the foregoing Patent 3, the tensile strengthis improved but the elongation and fracture toughness value are lowered.In Example 3, both the tensile strength and elongation are improved,which is probably due to that the heating in an inert gas and thesubsequent degassing in vacuum are carried out in this Example. However,it is assumed that an ordinary heat treatment (T7) is finally carriedout in this Example and the effect of the rapid heating is decreased tohalf.

The inventors have made various examinations as to methods whereby asufficient degassing can be carried out in economical manner even whenusing a rapid heating and consequently, have found that this problem canbe solved by utilizing the hydrogen gas evolved by the above describedrelease reaction. The above described generation of hydrogen gas takesplace, in particular, at a high temperature. The amount of the thusgenerated hydrogen gas, depending on the heating temperature, isgenerally about 30 ppm. There are pores of about 25% in a green compactof the powder and the volume of the hydrogen generated amounts to about10 times as much as that of the pores. In this case, it is required tohold the generated hydrogen in the pores of the green compact and tointroduce an inert gas into around the green compact without stirringthe atmosphere, in particular, to maintain a stagnant atmosphere, so asto impart to the hydrogen a function of turning out harmful steam oroxygen present in the pores of the green compact and allowing theforegoing reactions to proceed. Furthermore, in order to generate thehydrogen in a large amount at once, the heating at a temperature of atleast 300° C. for generating hydrogen should be carried out at a rate ofat least 0.4° C./sec, and in order to generate hydrogen in a largeamount in a series of the degassing reactions, it is required to heat upto a temperature of as higher as possible. Therefore, the heatingtemperature should be a temperature of at least 30° C., preferably atleast 50° C. higher than that of the vacuum degassing carried out beforeextrusion in the prior art (generally heated at about 450° C.). In thisway, the structure of the powder surface tends to be fixedly bonded. Asa measure of the tendency of bonding of the powder, it is required thatthat the amount of the residual hydrogen is at most 10 ppm.

When the heating temperature is higher, the structure of the interiorpart of the powder tends to be coarse even if rapid heating is effectedand it is required to carry out (i) heating in a short time, (ii)solidifying in a short time and (iii) quenching after solidifying.

(i) For the purpose of rendering most advantageous "heating in a shorttime", it is necessary to make an object to be heated as smaller aspossible. In this respect, in the extrusion method, the end part andresidual part are discarded and a large green compact is used to obtaina plurality of products in one extrusion and to increase the yield, sothat the rapid heating is naturally limited. On the other hand, in thepresent invention, one green compact is small and the rapid heating ispossible. A green compact is generally subjected to CIP (cold isotacticpressing), but in the powder forging, a uniaxial compression method by ametallic mold is applied. In this case, shearing of the powder acts eachother more effectively when compressed uniaxially than when compressedisotropically and contact of the powder grains is increased by the newlyexposed surfaces. Thus, inductive eddy current is increased and heatgenerated in the vicinity of the compact surface is more rapidlypropagated to the interior part. Therefore, the forging method is moreadvantageous in this respect.

(ii) The most effective solidifying method for solidifying in a shorttime is also the powder forging method. The time required for powderforging is about 0.7 second as compared with about 5 minutes requiredfor extrusion and about 20 minutes required for HIP (hot isotacticpressing).

(iii) For quenching after solidifying, it is required to separate aproduct from a tool used for working after hot working and powderforging is advantageous for this purpose. As to the cooling rate, about100° C./sec can be accomplished by water cooling, but in this case,there is a fear of cracking, in particular, when using a brittlematerial. In such a case, blowing-against of cooling air (cooling rateof about 10° to 20° C./sec) should be carried out and the cooling rateis thus adjusted to at least 10 ° C./sec. Since it is thought that asufficient solution treatment cannot be effected sometimes by onlydirect cooling after forging in the case of alloys of heat treatmenttype, it is preferable to reheat just after forging, rather thanreheating after cooling to room temperature, so as to reduce the thermalhistory to as small as possible during the same time. The reheatingtemperature during the same time is specified to at most the forgingtemperature to (the forging temperature -50° C.) for the purpose ofpreventing generation of blisters and obtaining a sufficient annealing.

When plastic working is carried out after solidifying in order to reducethe thermal history, moreover, heating is necessary for the plasticworking. Accordingly, this is not preferable. An organic lubricant isnot added because of lowering the heat conductivity during heating thegreen compact and hindering rapid rising of the temperature by theevaporation heat thereof. The rapid heating is most preferably carriedout by induction heating, but can also be carried out by irradiationheating or direct electric heating.

A solidified body according to the present invention has a feature suchas to be more changeable (concerning the structure distribution of aprecipitate, obtained by X-ray diffraction, shape of a precipitate, sizeof a precipitate -tendency of coarsening-) for a same composition at ahigh temperature (substantially same as the powder forging temperature)because of containing more non-equilibrium phases, than those preparedby other methods. When a powder is heated for a long time in an inertgas and then subjected to extrusion or powder forging so as to turn outthe air (predominantly consisting of nitrogen) contained in pores orgaps by hydrogen released from the powder surface, N₂ or Ar element canbe detected, while in the solidified body of the present invention, suchelements are contained only in an amount of at most the detectablelimit.

The degassed powder obtained according to the present invention, havingsuch a clean surface as having little adsorbed water or crystallinewater, can be subjected to powder forging as heated. Accordingly, thisis forged by a known forging method just after degassing. However, aninduction heating has the disadvantage that the temperature of a body tobe heated is more nonuniform as compared with an ordinary atmosphericheating furnace and accordingly, when the temperature gradient is large,the temperature thereof can be rendered uniform by holding at apredetermined temperature in an atmospheric heating furnace aftertemperature raising, during which the atmosphere should be of an inertgas.

The preform rapidly heated and degassed in this way is immediatelycharged in a metallic mold at about 200° C. and subjected to forging ata compacting pressure of 2 to 12 tons/cm².

EXAMPLES

The present invention will now be ilustrated in detail by the followingexamples without limiting the same. In the following ExperimentalExamples and Examples, an induction heating is carried out by about 3kHz.

Experimental Example A

About 250 g of an air-atomized powder (mean grain diameter: about 50 μm)with a composition of Al-25Si-2.5Cu-1Mg (by weight) was compacted at acompacting pressure of 4 tons/cm² in a diameter 100 mm×height 20 mm togive a specific electric resistance of 0.02 Ωcm, heated to 500° C. underthe following conditions A-1) to A-5), removed into a can having an Aratmosphere when the heating was finished, cooled to 50° C. within 1minute in an Ar stream, and then subjected to measurement of thequantity of oxygen and the quantity of hydrogen in the powder, thehardness (mHv) and the grain diameter of primary crystal Si. The resultsare shown in Table 1.

    ______________________________________                                        A-1) Induction heating in the air (32° C./sec)                                                     Present Invention                                 A-2) Induction heating in the air                                                                         Present Invention                                      (8.0° C./sec)                                                     A-3) Induction heating in the air                                                                         Present Invention                                      (4.0° C./sec)                                                     A-4) Induction heating in the air                                                                         Present Invention                                      (0.8° C./sec)                                                     A-5) Induction heating in the air                                                                         Outside Present                                        (0.2° C./sec)   Invention                                         For comparison, the same compacted body was heated to 500° C.          under the following conditions A-6) to A-8) using a resistance                heating furnace.                                                              A-6) Resistance furnace heating in vacuum                                                                 Outside Present                                        (maintained for 1 hour)                                                                              Invention                                         A-7) Resistance furnace heating in N.sub.2                                                                Outside Present                                        atmosphere (maintained for 1 hour)                                                                   Invention                                         A-8) Resistance furnace heating in the air                                                                Outside Present                                        (maintained for 1 hour)                                                                              Invention                                         ______________________________________                                    

The properties of the alloy powders thus obtained are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Heating                                                                              Oxygen   Hydrogen  Powder Primary Crystal                              Con-   Quantity Quantity  Hardness                                                                             Si Grain Diameter                            ditions                                                                              (wt %)   (ppm)     (mHv)  (μm)                                      ______________________________________                                        Within                                                                        Present                                                                       Invention                                                                     A-1    0.27     3         172     3.2                                         A-2    0.28     4         153     3.1                                         A-3    0.30     3         130     4.0                                         A-4    0.28     5         115     7.8                                         Outside                                                                       Present                                                                       Invention                                                                     A-5    0.33     6         100    10.2                                         A-6    0.28     3          92    11.2                                         A-7    0.28     9          95    10.7                                         A-8    0.38     17        102    10.0                                         ______________________________________                                         Note 1: Powder Hardnes (mHv): mean value of five points                       Note 2: Primary Crystal Si Grain Diameter: mean value of thirty samples  

From the results of Table 1, it is apparent that 1) the degree ofdegassing can substantially be obtained as in degassing in vacuum and 2)the structure is not coarsened and the hardness is high because oflittle thermal history.

Experimental Example B

The procedures under the conditions of Experimental Examples A-1), A-4),A-5), A-7) and A-8) were repeated except using a mixed powder ofair-atomized, industrial grade pure aluminum powder (mean graindiameter: 50 μm) and 30 volume % of SiC grains with a mean graindiameter of 1.5 μm, as a raw material powder. The properties of theresulting powders are shown in Table 2, in which the powder hardness ismasured as to the aluminum powder.

                  TABLE 2                                                         ______________________________________                                                                                Primary                                                                       Crystal                               Experi-                                                                              Heating  Oxygen   Hydrogen                                                                              Powder Si Grain                              mental Con-     Quantity Quantity                                                                              Hardness                                                                             Diameter                              Example                                                                              ditions  (wt %)   (ppm)   (mHv)  (μm)                               ______________________________________                                        Within                                                                        Present                                                                       Invention                                                                     B-1    A-1      0.20     4       95     --                                    B-2    A-4      0.19     5       93     --                                    Outside                                                                       Present                                                                       Invention                                                                     B-3    A-5      0.26     7       85     --                                    B-4    A-7      0.21     8       63     --                                    B-5    A-8      0.32     15      62     --                                    ______________________________________                                         Note 1: Powder Hardness (mHv): mean value of five points                 

Experimental Example C

The procedures under the conditions of Experimental Examples A-1), A-4),A-5), A-7) and A-8) were repeated except using a mixed powder ofair-atomized, Al-20Si-5Fe-2Ni alloy powder (mean grain diameter: 50 μm)and alumina powder with a mean grain diameter of 0.5 μm, as a rawmaterial powder. The properties of the resulting powders are shown inTable 3. The quantity of oxygen is a quantity from which the quantity ofoxygen contained in the alumina grains has been removed by calculation.The powder hardness is masured as to the aluminum alloy powder.

                  TABLE 3                                                         ______________________________________                                                                                Primary                                                                       Crystal                               Experi-                                                                              Heating  Oxygen   Hydrogen                                                                              Powder Si Grain                              mental Con-     Quantity Quantity                                                                              Hardness                                                                             Diameter                              Example                                                                              ditions  (wt %)   (ppm)   (mHv)  (μm)                               ______________________________________                                        Within                                                                        Present                                                                       Invention                                                                     C-1    A-1      0.26     4       186    2.6                                   C-2    A-4      0.29     3       179    2.4                                   Outside                                                                       Present                                                                       Invention                                                                     C-3    A-5      0.32     5       145    5.6                                   C-4    A-7      0.28     10      108    6.8                                   C-5    A-8      0.40     19      113    6.5                                   ______________________________________                                         Note 1: Powder Hardness (mHv): mean value of five points                      Note 2: Primary Crystal Si Grain Diameter: mean value of thirty samples  

Experimental Example D

About 500 g of an air-atomized powder with a composition ofAl-20Si-5Fe-1Ni (mean grain diameter: 50 μm) was compacted in a diameterof 100 mm and height of 40 mm while varying the compacting density asshown in Table 4, and then subjected to measurement of the specificelectric resistance. In the central part and outer circumferential partof the green compact were respectively made two holes each having adiameter of 1.0 mm in which a thermocouple is to be inserted and thetemperature raising gradient was sought in which the temperaturegradient between both the sites was not 70° C. or higher and the fastesttemperature raising could be obtained.

                  TABLE 4                                                         ______________________________________                                               Specific     Maximum Temperature-Raising                                      Electric     Gradient in Which Temperature                             Green  Resistance of                                                                              Gradient between Central Part and                         Compact                                                                              Green Compact                                                                              Peripheral Part of Green Compact                          No.    (Ω cm) is not 70° C. or Higher (°C./sec)           ______________________________________                                        D-1     0.001       25                                                        D-2     0.005       16                                                        D-3     0.01        8                                                         D-4     0.02        3.2                                                       D-5     0.05        2                                                         D-6    0.1          0.9                                                       D-7    0.2          0.4                                                       D-8    0.5          0.2                                                       D-9    1.0          0.09                                                       D-10  2.0          not reached 500° C.                                ______________________________________                                         As shown in Table 4, the temperatureraising efficiency is not good at a       specific electric resistance of about 0.2Ω cm or more.             

EXAMPLE 1

An air-atomized powder (mean grain diameter: about 50 μm) with acomposition of Al-25Si-2.5Cu-1Mg (by weight, same hereinafter) wascompacted in a diameter 100 mm×height 20 mm to give a specific electricresistance of 0.02 Ωcm and heated in the air to 500° C. from roomtemperature for 4 minutes by induction heating. The product wasimmediately charged in a metallic mold (200° C.) lined with graphitelubricant, powder-forged at a compacting pressure of 8 tons/cm² and justafter the forging, cooled by immersing in water at room temperature. Theforeged body was subjected to natural ageing for 4 days, after whichRockwell hardness B scale (H_(R) B) was measured to obtain an H_(R) B of86.

For comparison, the green compact prepared in the similar manner toExample 1 was heated for 1 hour in a nitrogen atmosphere at 500° C. in aresistance furnace and after heating, forged, cooled and then subjectedto natural ageing and measurement of the hardness to obtain an H_(R) Bof 79 (Comparative Example 1).

EXAMPLE 2

250 g of an air-atomized powder (mean grain diameter: about 50 μm) witha composition of Al-25Si-2.5Cu-1Mg was compacted at a compactingpressure of 4 tons/cm² in a diameter 100 mm×height 20 mm to give aspecific electric resistance of 0.02 Ωcm, heated to 500° C. under thefollowing conditions 2-1) to 2-5), charged into a mold heated at 200° C.when the heating was finished, subjected to powder forging at acompacting pressure of 8 tons/cm², immediately cooled by immersing inwater. Therefore, the product was subjected to natural ageing for 4days.

In the case of 2-3'), "moistened", the green compact was exposed to anatmosphere at a temperature of 40° C. and a humidity of 90% for 24hours, before heating and degassing, thus adsorbing a large amount ofwater on the surface of the powder, and then subjected to the stepsafter the heating and degassing in the similar manner.

    ______________________________________                                        2-1) Induction heating in air (32° C./sec)                                                         Present Invention                                 2-2) Induction heating in the air                                                                         Present Invention                                      (8.0° C./sec)                                                     2-3) Induction heating in the air                                                                         Present Invention                                      (4.0° C./sec)                                                     2-3')                                                                              Induction heating in the air moistened                                                               Present Invention                                      (4.0° C./sec)                                                     2-4) Induction heating in the air                                                                         Present Invention                                      (0.8° C./sec)                                                     2-5) Induction heating in the air                                                                         Outside Present                                        (0.2° C./sec)   Invention                                         ______________________________________                                    

For comparison, the same compact was heated to 500° C. under thefollowing conditions 2-6) to 2-7) using a resistance heating furnace,forged, then heated at 485° C. for 2 hours and immersed in water toeffect a solution treatment and thereafter, subjected to natural ageingfor 4 days.

    ______________________________________                                        2-6) Resistance furnace heating in N.sub.2                                                                Outside Present                                        atmosphere (maintained for 1 hour)                                                                   Invention                                         2-6')                                                                              Resistance furnace heating in N.sub.2                                                                Outside Present                                        atmosphere (maintained for 1 hour)                                                                   Invention                                              moistened                                                                2-7) Resistance furnace heating in the air                                                                Outside Present                                        (maintained for 1 hour)                                                                              Invention                                         2-7')                                                                              Resistance furnace heating in the air                                                                Outside Present                                        (maintained for 1 hour) moistened                                                                    Invention                                         ______________________________________                                    

The properties of the alloy powders thus obtained are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________           Degassing Conditions                                                   Sample No.                                                                           Heating Means                                                                           Atmosphere                                                                             Temperature Conditions                                                                      Moistened                             __________________________________________________________________________    Example                                                                       2-1    Induction Heating                                                                       In The Air                                                                             Temp. Raising at 32° C./sec                                                          No                                    2-2    Induction Heating                                                                       In The Air                                                                             Temp. Raising at 8.0° C./sec                                                         No                                    2-3    Induction Heating                                                                       In The Air                                                                             Temp. Raising at 4.0° C./sec                                                         No                                    2-3'   Induction Heating                                                                       In The Air                                                                             Temp. Raising at 4.0° C./sec                                                         Yes                                   2-4    Induction Heating                                                                       In The Air                                                                             Temp. Raising at 8.0° C./sec                                                         No                                    Comparative                                                                   Example                                                                       2-5    Induction Heating                                                                       In The Air                                                                             Temp. Raising at 0.2° C./sec                                                         No                                    2-6    Resistance Furnace                                                                      In N.sub.2 Atmosphere                                                                  Maintained For 1 Hour                                                                       No                                           Heating                                                                2-6'   Resistance Furnace                                                                      In N.sub.2 Atmosphere                                                                  Maintained For 1 Hour                                                                       Yes                                          Heating                                                                2-7    Resistance Furnace                                                                      In The Air                                                                             Maintained For 1 Hour                                                                       No                                           Heating                                                                2-7'   Resistance Furnace                                                                      In The Air                                                                             Maintained For 1 Hour                                                                       Yes                                          Heating                                                                __________________________________________________________________________            Properties of Forged Body                                                     Amount of                                                                            Amount of                                                                              Tensile Strength                                                                       Elongation                                                                           Hardness                              Sample No.                                                                            Oxygen (%)                                                                           Hydrogen (ppm)                                                                         (kg/mm.sup.2)                                                                          (%)    H.sub.R B                             __________________________________________________________________________     Example                                                                      2-1     0.23   3        48       1.2    89                                    2-2     0.30   4        50       2.0    85                                    2-3     0.29   3        52       3.0    86                                     2-3'   0.76   4        51       1.8    88                                    2-4     0.32   5        50       1.8    85                                    Comparative                                                                   Example                                                                       2-5     0.38   8        45       1.0    83                                    2-6     0.28   9        49       1.8    87                                     2-6'   0.38   11       32       0.2    82                                    2-7     0.42   17       30       0.0    75                                     2-7'   0.93   23       23       0.0    65                                    __________________________________________________________________________

From the results of Table 5, it is apparent that according to thepresent invention, degassing is well carried out and forged bodieshaving well balanced properties such as hardness, tensile strength,elongation, etc. are obtained without deteriorating the quenching effectof the raw material powder because of the small thermal history.

In comparison of the results of 2-3') and 2-6'), it is apparent that inthe effective degassing method of the present invention, degassing(removal of adsorbed water) can sufficently be carried out even if thereis a large amount of adsorbed water (becoming crystalline water ofalumina during heating), while in the degassing method 2-6') of theprior art, it is difficult to remove such a large amount of the adsorbedwater and the resulting forged body has inferior properties.

The forged bodies obtained in Examples 2-1) and 2-3) according to thepresent invention and Comparative Example 2-6) according to the priorart, as dsecribed above, were cut and polished, and then after etchingstrongly, subjected to observing of the structure thereof by SEM(scanning electron microscope), thus obtaining SEM photographs as shownin FIG. 1 to FIG. 3. It is apparent from these photographs that thestructures of the forged bodies according to the present invention areclearly finer than that of the prior art.

EXAMPLE 3

The procedures under the conditions of Examples 2-1) and 2-4) andComparative Examples 2-6) and 2-7) were repeated except using a mixedpowder of air-atomized, Al-20Si-5Fe-2Ni alloy powder (mean graindiameter: 50 μm) and alumina powder with a mean grain diameter of 0.5μm, as a raw material powder, thus obtaining forged bodies 3-1) and 3-2)of the present invention and comparative articles 3-3) and 3-4). Theproperties measured in the similar manner to Example 2 are shown inTable 6. The quantity of oxygen is a quantity from which the quantity ofoxygen contained in the alumina grains has been removed by calculation.

                                      TABLE 6                                     __________________________________________________________________________                 Amount of                                                                           Amount of                                                                           Tensile                                                     Heating                                                                             Oxygen                                                                              Hydrogen                                                                            Strength                                                                            Elongation                                                                          Hardness                                        Condition                                                                           (%)   (ppm) (kg/mm.sup.2)                                                                       (%)   H.sub.R B                                __________________________________________________________________________    Example                                                                       3-1    2-1   0.26   4    62    0.8   108                                      3-2    2-4   0.35   3    59    0.6   110                                      Comparative                                                                   Example                                                                       3-3    2-6   0.25  10    48    0.4    89                                      3-4    2-7   0.53  19    28    0.0    68                                      __________________________________________________________________________

It is apparent from the results of Table 6 that the forged bodies of thepresent invention have good properties.

EXAMPLE 4

The procedures under the conditions of Examples 2-1) and 2-4) andComparative Examples 2-6) and 2-7) were repeated except using anair-atomized, Al-12Si- 5 vol % (mean grain diameter: 2 μm) SiC aluminumcomposite alloy powder (mean grain diameter: 50 μm) as a raw materialpowder, thus obtaining forged bodies 4-1) and 4-2) of the presentinvention and comparative articles 4-3) and 4-4). The propertiesmeasured in the similar manner to Example 2 are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Heat-   Amount   Amount                                                       ing     of       of Hy-   Tensile Elonga-                                                                              Hard-                                Condi-  Oxygen   drogen   Strength                                                                              tion   ness                                 tion    (%)      (ppm)    (kg/mm.sup.2)                                                                         (%)    H.sub.R B                            ______________________________________                                        Example                                                                       4-1 2-1     0.26      4     62      0.8    108                                4-2 2-4     0.35      3     59      0.6    110                                Comparativ Example                                                            4-3 2-6     0.25     10     48      0.4     89                                4-4 2-7     0.53     19     28      0.0     68                                ______________________________________                                    

It is apparent from the results of Table 7 that the forged bodies of thepresent invention have good properties.

EXAMPLE 5

About 250 g of an air-atomized powder (mean grain diameter: about 50 μm)with a composition of Al-25Si-2.5Cu-1Mg was compacted at a compactingpressure of 4 tons/cm² in a diameter 100 mm×height 20 mm to give aspecific electric resistance of 0.02 Ωcm, heated to 500° C. under thefollowing conditions 5-1) to 5--5), charged into a mold heated at 200°C. when the heating was finished, subjected to powder forging at acompacting pressure of 8 tons/cm², immediately cooled by immersing inwater. Therefore, the product was subjected to natural ageing for 4days.

    ______________________________________                                        5-1)   Induction heating in the air (32° C./sec) . . . Present                Invention                                                              5-2)   Induction heating in the air (8.0° C./sec) . . . Present               Invention                                                              5-3)   Induction heating in the air (4.0° C./sec) . . . Present               Invention                                                              5-4)   Induction heating in the air (0.8° C./sec) . . . Present               Invention                                                              5-5)   Induction heating in the air (0.2° C./sec) . . . Outside               Present Invention                                                      ______________________________________                                    

For comparison, the same compact was heated to 500° C. under thefollowing conditions 5-6) using a resistance heating furnace, forged,then heated at 485° C. for 2 hours and immersed in water to effect asolution treatment and thereafter, subjected to natural ageing for 4days.

    ______________________________________                                        5-6)  Resistance furnace heating in N.sub.2 atmosphere                              (maintained for 1 hour) . . . Outside Present Invention                 5-7)  Resistance furnace heating in the air                                         (maintained for 1 hour) . . . Outside Present Invention                 5-8)  Resistance furnace heating in vacuum                                          (maintained for 1 hour)                                                       moistened . . . Outside Present Invention                               ______________________________________                                    

The properties of the alloy powders thus obtained are shown in Table 8.From the results of Table 8, it is apparent that according to thepresent invention, forged bodies having well balanced properties such ashardness, tensile strength, elongation, etc. are obtained withoutdeteriorating the quenching effect of the raw material powder because ofthe good degassing and small thermal history of the aluminum alloypowder forged body according to the present invention.

                                      TABLE 8                                     __________________________________________________________________________    Degassing Conditions                                                          Sample No.                                                                          Heating Means                                                                           Atmosphere                                                                             Temperature Conditions                                                                      Moistened                              __________________________________________________________________________    Example                                                                       5-1   Induction Heating                                                                       In The Air                                                                             Temp. Raising at 32° C./sec                                                          No                                     5-2   Induction Heating                                                                       In The Air                                                                             Temp. Raising at 8.0° C./sec                                                         No                                     5-3   Induction Heating                                                                       In The Air                                                                             Temp. Raising at 4.0° C./sec                                                         No                                     5-4   Induction Heating                                                                       In The Air                                                                             Temp. Raising at 0.8° C./sec                                                         No                                     Comparative Example                                                           5-5   Induction Heating                                                                       In The Air                                                                             Temp. Raising at 0.2° C./sec                                                         No                                     5-6   Resistance Furnace                                                                      In N.sub.2 Atmosphere                                                                  Maintained For 1 Hour                                                                       No                                           Heating                                                                 5-7   Resistance Furnace                                                                      In The Air                                                                             Maintained For 1 Hour                                                                       No                                           Heating                                                                 5-8   Resistance Furnace                                                                      In Vacuum                                                                              Maintained For 1 Hour                                                                       No                                           Heating                                                                 __________________________________________________________________________    Properties of Forged Body                                                              Amount of                                                                             Amount of                                                                           Tensile                                                         Oxygen  Hydrogen                                                                            Strength                                                                            Elongation                                                                          Hardness                                   Sample No.                                                                             (%)     (ppm) (kg/mm.sup.2)                                                                       (%)   H.sub.R B                                  __________________________________________________________________________    Example                                                                       5-1      0.26    4     52    1.0   99                                         5-2      0.29    4     55    1.2   98                                         5-3      0.30    3     58    1.8   98                                         5-4      0.35    5     57    2.0   83                                         Comparative Example                                                           5-5      0.40    8     51    1.5   80                                         5-6      0.27    8     19    0.0   73                                         5-7      0.45    20    *     *     65                                         5-8      0.38    3     42    0.0   83                                         __________________________________________________________________________

EXAMPLE 6

An atomized powder with a composition of Al-25Si-2.5Cu-1Mg (by weight %)was formed in a shape of φ 50 mm×50 mm t under a pressure of 4 tons/cm²by a die wall lubricating mold, heated to a forging temperature for 4minutes by induction heating and forged in a shape of φ 53 mm. Theforging conditions were a heating temperature of 500° C. and a forgingpressure of 5 tons/cm².

After the forging, the product was subjected to a T6 heat treatment(comprising holding at 490° C. for 1.5 hours, immersing in water andsubjecting to an ageing treatment at 180° C. for 6 hours) and subjectedto estimation of the strength. The tensile strength was estimated in n=2to obtain 53 kg/mm² and 51 kg/mm².

For comparison, the same powder was subjected to powder forging bymixing with a lubricant and heating in an electric furnace, thusobtaining a tensile strength of 48 kg/mm² in n=2.

It will be understood from these results that better results areobtained when a raw material powder is previously formed without addinga lubricant thereto and coating an inner wall of a mold.

The foregoing Examples have been given exemplifying the rapidlysolidified powder, but the method of the present invention can also beapplied to degassing of other powders than the rapidly solidified powderwith a merit of lowering of the production cost.

EXAMPLE 7

A gas atomized powder (Al-7.3Ni-2.9Fe) was pressed at a compactingpressure of 4 tons/cm² to prepare three samples each having a shape of φ70 mm×25 mmt, heated to 550° C. for 2 minutes by induction heating forone sample, by radiation heating for another sample and by directelectric heating for a further sample, and then forged in φ 72 mm at aforging pressure of 8 tons/cm² and after the forging, water-cooled. Theproperties of the products at room temperature were as follows:

Induction-heated product: tensile strength 62.3 kg/mm², elongation13.5%,

    K.sub.lc 28.0 kg/mm.sup.2 √m

Radiation-heated product: tensile strength 60.1 kg/mm², elongation13.0%,

Direct electrically-heated product: tensile strength 63.4 kg/mm²,elongation

    13.6%

EXAMPLE 8

A gas atomized powder (Al-8.8Fe-3.7Ce) was pressed at a compactingpressure of 4 tons/cm² to prepare a samples having a shape of φ 70 mm×25mm t, induction-heated to 550° C. for 1.5 minutes and then forged in φ72 mm at a forging compacting pressure of 8 tons/cm² and after theforging, water-cooled. The properties of the product at room temperaturewas as follows:

Tensile strength: 65.2 kg/mm² and elongation: 16.2%

EXAMPLE 9

A gas atomized powder (Al-8Zn-2.5Mg-1Cu-1.6Co) was pressed at acompacting pressure of 4 tons/cm² to prepare a sample having a shape ofφ 70 mm×25 mm t, induction-heated to 530° C. for 1 minute and thenforged in φ 72 mm at a forging pressure of 8 tons/cm². After theforging, the temperature was lowered to 460° C. and accordingly, theproduct was reheated to 520° C. in 1 minute by induction heating,water-cooled and subjected to natural ageing for 4 days, followed byexamining the properties at room temperature.

Tensile strength: 70.2 kg/mm² and elongation: 12.5%

EXAMPLE 10

10 g of an air-atomized powder with a composition of Al-25Si-3Cu-1Mg wascompacted at a compacting pressure of 4 tons/cm² in a shape of 10×18×30mm and heated to 510° C. for 4 minutes by an infrared radiation heatingin the stagnant atmosphere, followed by forging. A metallic mold of10.5×10.5 mm was used at a mold temperature of 400° C.. The forgingpressure was 8 tons/cm². After the forging, the product was water-cooledand then subjected to examination of the properties without heattreatment.

Tensile strength: 58 kg/cm², fracture elongation: 3.0% (at roomtemperature)

The same green compact was heated to 510° C. for 4 minutes in a nitrogenstream (7 liters/min) and then forged under the same conditions asdescribed above.

Tensile strength: 51 kg/cm², fracture elongation: 2.1% (at roomtemperature)

EXAMPLE 11

20 kg of an air-atomized powder with a composition ofAl-17Si-5Fe-3Cu-1Mg was subjected to CIP (compacting pressure: 2tons/cm²) to prepare a green compact with a dimension of φ 180×300 mm.

The resulting compact was subjected to:

    ______________________________________                                        1 ambient heating in N.sub.2 atmosphere                                                           (450° C. × 4 hours)                                              (490° C. × 4 hours)                          2 induction heating in the air                                                                    (temperature raising to                                                       460° C. in 16 minutes)                                                 (temperature raising to                                                       500° C. in 16 minutes)                             ______________________________________                                    

These samples were extruded in φ 44 (extrusion ratio: 21) by a containerwith a diameter of φ 200, cooled after the extrusion and subjected toexamination of the properties of a F material and then to a T6 treatment(470° C. ×2 hours→water-cooled 175° C.×6 hours) to examine theproperties thereof.

Furthermore, after the extrusion, the sample was charged in a furnace at485° C. for 10 minutes, water-cooled, subjected to an ageing treatmentof 175° C.×6 hours and reheated to obtain a T6 material.

3. Similarly, 250 g of the powder was compacted in φ 80 mm (metallicmold with lubricating wall: pressure 4 tons/cm²), induction-heated inthe air(temperature raising of to 520° C. in 2.5 minutes), charged in ametallic mold with φ 82 and subjected to powder forging at a pressure of8 tons/cm². After the forging, the product was immediately water-cooledto obtain a F material.

After the forging, the product was induction-heated to 485° C. for 1minute, water-cooled and subjected to an ageing treatment of 175° C.×6hours to obtain a rapidly reheated T6 material.

After the forging, the product was charged in a furnace at 485° C. for10 minutes, water-cooled and subjected to an ageing treatment of 175°C.×6 hours to obtain a reheated T6 material.

After the forging, the product was directly water-cooled and thensubjected to a T6 treatment (i.e. subjected to 485° C.×2 hours,water-cooling and a treatment of 175° C.×6 hours) to obtain a T6material.

The above described samples were subjected to examination of theproperties, thus obtaining results shown in Table 9.

                                      TABLE 9                                     __________________________________________________________________________                 Heating Tensile                                                                            Elonga-                                                                            Amount of                                      Sample                                                                            Solidified                                                                             Temp.   Strength                                                                           tion Hydrogen                                       No. Material (°C.)                                                                       H.sub.R B                                                                        (kg/cm.sup.2)                                                                      (%)  (ppm) Remarks                                  __________________________________________________________________________    1   1-F material                                                                           450  78 45   0.4  18    A                                        2   1-T6 material 88 49   1.0  --    A                                        3   1-F material                                                                           490  75 41   1.4  15    A                                        4   1-T6 material 85 43   1.2  --    A                                        5   2-F material                                                                           460  89 53   1.3  14    A                                        6   2-Reheated T6 93 55   0.9  --    A                                        7   2-T6 material 92 50   1.1  --    A                                        8   2-F material                                                                           500  88 57   2.6   9    B                                        9   2-Reheated T6 91 59   2.1  --    B                                        T6 material  89   54 1.8  --   B                                              F material                                                                        520      92   61 2.8   7   B                                              Rapidly      96   62 2.2  --   B                                                  Reheated T6                                                               Reheated T6  93   60 2.0  --   B                                              T6 material  88   57 1.9  --   B                                              __________________________________________________________________________     Note)                                                                         1˜3 of Solidified Material correspond to the treatments                 1˜3 in Example 11.                                                      A: Comparative Example                                                        B: Example                                                               

The following matters are apparent from the foregoing results.

(1) In extrusions, the rapidly heating method according to the presentinvention is also useful.

(2) The product obtained by rapidly heated to a lower temperature in theextrusion exhibits a smaller elongation.

(3) The product obtained by rapidly heated to a lower temperature in theextrusion exhibits a larger amount of hydrogen.

(4) When rapidly heating and extruding according to the presentinvention, the reheated T6 gives better properties than the ordinary T6.

(5) Even the F material gives sufficient properties when rapidly heatingand powder forging according to the present invention.

(6) When rapidly heating and powder forging according to the presentinvention, the reheated T6 material gives better properties than the T6material and the rapidly reheated T6 material gives better propertiesthan the reheated T6 material.

(7) In the articles of the present invention, both the tensile strengthand fracture elongation can simultaneously be improved more than theprior art materials.

EXAMPLE 12

The above described Sample Nos. 2 and 11 were subjected to examinationof the tensile strength and elongation at 300° C.:

    __________________________________________________________________________    Sample No. 2                                                                          Material . . . 22 kg/mm.sup.2, 3.5% elongation                                                    Comparison                                        Sample No. 11                                                                         Material . . . 28 kg/mm.sup.2, 5.6% elongation                                                    Present Invention                                 __________________________________________________________________________

Accordingly, it is apparent that the article of the present invention isalso excellent in heat resistance.

EXAMPLE 13

250 g of a rotary disk atomized powder with a composition of Al-8Fe-4Mowas compacted in φ 80 mm (metallic mold with lubricating wall surface)and heated under following conditions:

    ______________________________________                                        induction heating in the air                                                                 (temperature raising to 510° C. in 1.0                                 minute)                                                                       (temperature raising to 650° C. in 1.0                                 minute)                                                        ______________________________________                                    

The product was charged in a metallic mold of φ 82 mm and subjected topowder-forging at a pressure of 8 tons/cm². After the forging, theproduct was cooled to examine the properties. The results are shown inTable 10.

                  TABLE 10                                                        ______________________________________                                        Heating Temperature                                                                        Tensile Strength                                                                           Fracture Elongation                                 (°C.) (kg/mm.sup.2)                                                                              (%)                                                 ______________________________________                                        510          67           4.5                                                 650          66           12.3                                                ______________________________________                                    

As described above, in an aluminum alloy with a high melting point,heating at a temperature exceeding 600° C. gives sometimes good results.

Utility and Possibility on Commercial Scale

Since according to the present invention, a sufficient degassing can becarried out in simpler steps and more economical manner and with a lowerthermal history than in the prior art, all the tensile strength,elongation and fracture toughness value can be improved without carryingout heating in an inert atmosphere, degassing in vacuum and plasticdeformation after solidifying. Thus, the method of the present inventionis useful for the industry.

We claim:
 1. A method of degassing an aluminum alloy powder,characterized by preforming an aluminum powder, aluminum alloy powder oraluminum composite alloy powder or mixed powders thereof withnon-metallic grains to give a specific electric resistance of at most0.2Ωcm, subjecting the preform directly to induction heating in anatmosphere at normal pressure, temperature-raising to 400° to 600° C. ata temperature gradient of at least 0.4° C./sec in a temperature range ofat least 300° C., and removing heat-decomposable volatile components toobtain a hydrogen content of at most 10 ppm.
 2. The method of degassingan aluminum alloy powder, as claimed in claim 1, wherein the inductionheating is carried out in the air.
 3. The method of degassing analuminum alloy powder, as claimed in claim 1 or claim 2, wherein afterdegassing by the induction heating, the preform is cooled in an inertgas atmosphere.
 4. A method of solidifying a rapidly solidified aluminumalloy powder, characterized by preforming an aluminum powder, aluminumalloy powder or aluminum composite alloy powder or mixed powders thereofwith non-metallic grains to give a specific electric resistance of atmost 0.2 Ωcm, subjecting the preform directly to induction heating in astagnant atmosphere at normal pressure, maintaining atemperature-raising gradient of at least 0.4° C./sec at a temperaturerange of at least 300° C., temperature-raising to 400° to 600° C.corresponding to a temperature of at least 30° C. higher than the vacuumdegassing temperature applied to a case of extruding the above describedpowder, removing heat-decomposable volatile components to obtain ahydrogen content of at most 10 ppm, then directly subjecting a productto hot working and solidifying the product.
 5. The method of solidifyinga rapidly solidified aluminum alloy powder, as claimed in claim 4,wherein the temperature raised by the induction heating is in the rangeof 400° C. to the melting point.
 6. The method of solidifying a rapidlysolidified aluminum alloy powder, as claimed in claim 4 or claim 5,wherein the hot working is a powder forging.
 7. The method ofsolidifying a quenched aluminum alloy powder, as claimed in claim 4,wherein the induction heating is carried out in the stagnant atmosphere.8. The method of solidifying a rapidly solidified aluminum alloy powder,as claimed in claim 4 or claim 5, wherein immediately after forging, theproduct is quenched at a rate of at least 10° C./sec or reheated at atemperature of at most the forging temperature to at least (the forgingtemperature -50° C.) without cooling to room temperature, thus effectingquenching and solution treatment.
 9. The method of solidifying a rapidlysolidified aluminum alloy powder, as claimed in any one of claims 4 to6, wherein the preforming of the powder is carried out by coating aninner wall of a forming metallic mold with a wetting agent withoutadding an organic wetting agent to the powder.
 10. The method ofsolidifying a rapidly solidified aluminum alloy powder, as claimed inany one of claims 4 to 7, wherein a radiation heating or direct electricheating is used instead of the induction heating.